EN
EN
**Behro Comprehensive Consulting Engineers**
**Davood Parsapour, Dariush Mohammadi, Ahmad Fahimifar**
**13th Iran Tunnelling Conference**
**November 19, 2019**
In urban tunnelling projects, particularly in shallow areas and alluvial ground conditions, the selection of a tunnel alignment is often subject to significant constraints, making it sometimes unavoidable for tunnels to pass beneath sensitive surface structures. Mechanized tunnelling under such conditions requires careful control, as excavation-induced deformations can affect the stability of adjacent structures. This article investigates the effects of an **EPB tunnelling machine passing beneath the Pardisan gravity retaining wall** in the **Sanat Square area**, along a section of the **south–north alignment of Tehran Metro Line 7**. The study analyzes the **three-dimensional tunnel–soil–wall interaction** using the **finite element method (FEM)** in **PLAXIS**.
The results show that, contrary to the common assumption that the presence of a surface structure generally reduces settlement, the **Pardisan retaining wall** experienced greater settlement due to its relatively small width compared with the tunnel diameter. The numerical modelling indicates that the wall falls within the **“severe to very severe damage”** category, and the cracks observed in the wall also confirm the occurrence of the predicted analytical behavior. A parametric study further shows that various factors, including **over-excavation, face pressure, and grout injection pressure**, influence the settlement pattern. However, **over-excavation had the greatest effect on increasing settlement and differential settlement at the wall foundation**.
On the other hand, the results show that increasing the **wall foundation width** increases the structural stiffness and reduces settlement, whereas increasing the **wall height** leads to greater penetration due to the increase in weight and overturning moment. Changes in the **geometric position of the tunnel relative to the wall** can also reduce both the magnitude of settlement and its extent of influence. These findings highlight the importance of **accurate numerical modelling**, analysis of **soil–structure–tunnel interaction**, and appropriate selection of **control parameters for EPB tunnelling** to protect sensitive urban structures.
